1. Field of the Invention
The present invention relates to amplifier circuits, and is mainly devoted to a class "B" amplifier circuit composed of transistors.
2. Description of the Prior Art
The vertical deflection output circuit of a television receiver requires a vertical output deflection circuit having a large output such as a Braun tube with a wide deflection angle and a large screen diameter. A class "B" push-pull circuit has therefore been adopted as the output circuit.
The vertical deflection output circuit amplifies a vertical signal and a pulse for blanking the picture frame during the vertical retrace time, namely, the back pulse. In order to achieve the purpose mentioned above, the voltage amplitude of the back pulse must be high in comparison with that of the vertical signal. The supply voltage V.sub.CC of the output circuit is, accordingly, high in proportion to the required voltage of the back pulse.
At the output of the vertical deflection output circuit, however, the period during which the back pulse is provided is much shorter than the period during which the vertical signal is provided. This brings about the problem that the utilization factor of the supply voltage is extremely inferior and that the collector loss of a power transistor is very great.
As a method for solving this problem, there has hitherto been known one in which the back pulse is produced by a separate circuit and is added to the vertical signal. Since this method necessitates a pulse generator and an amplifier circuit for producing a back pulse of high voltage, the circuit arrangement becomes complicated.
On the other hand, in a sound output amplifier circuit, a class "B" amplifier circuit is generally adopted. When compared with a class "A" amplifier circuit, the class "B" amplifier circuit has a good utilization factor of the power source ##EQU1## AND LITTLE HEAT GENERATION, AND HENCE, IT IS SUITED FOR A LARGE OUTPUT AMPLIFIER CIRCUIT. Even in the case of a class "B" amplifier circuit, however, the utilization factor of power source is 70% or so for a maximum output, and is sharply lowered for small outputs. For this reason, in the case of an output amplifier circuit of large output, even the class "B" amplifier circuit generates a large amount of heat creating difficulties in the design of heat radiation.